1. Field of the Invention
The present invention relates to a method of coring a crustal core sample, which is available to, for example, researches on intracrustal microorganisms in the crustal core, and antimicrobial polymeric gel and a gel material used in this method.
2. Description of the Background Art
In recent years, researches on crustal interiors have been progressed, and a presence of subterranean microorganisms under a depth, high-temperature and high-pressure environments in the crustal interior has been reported. According to researches on intra-crustal microorganisms in a subterranean microbial sphere composed of these subterranean microorganisms, there are important hidden possibilities such as elucidation of influences of material conversion and mass transfer in a deep geological environment for example, and further, elucidation of origin of life on the primitive earth and evolution thereof, or development of drugs and novel materials.
A crustal core sample can be taken with comparative ease from the crust at the depth closer to mantle by drilling crust of sea bed by means of, for example, a drill ship. As an example of a method for conducting the drilling using the drill ship, for example, a riser drilling method has been known. In this method, a drill pipe extending from the drill ship to the sea bed is rotated to drill the crust by means of a drill bit provided on the tip thereof and at the same time, to feed circulating fluid such as drilling mud or sea water, in which the specific gravity, viscosity, chemical composition, etc. have been adjusted according to the condition of the crust drilled, to the drill bit.
A crustal core sample obtained by such a method has a great possibility that the state of the sample present in the crust as it is may be lost by an influence exerted from the outside during the coring operation, for example, by causes such as its contact with the circulating fluid. In such a case, there is a possibility that the crustal core sample obtained may become useless for various research objects.
In order to deal with such a problem, a method in which when a crustal core sample is cored, the surface thereof is coated with non-invasive gel, thereby obtaining the crustal core sample in a state that its physical structure has been protected from the external factor is disclosed in U.S. Pat. No. 5,482,123.
In this method, however, there is a possibility that adventitious heterogeneous microorganisms may permeate the gel coat on the surface of the core sample to enter the interior of the gel coat, thereby adhering to the crustal core sample. The microorganisms adhered, then may possibly grow on the surface or in the interior of the crustal core sample.
In the handling of the gel forming the surface coat, it is extremely difficult to prevent the gel from being contaminated with the microorganisms because the microorganisms unavoidably adhere to the gel itself.
The crustal core sample contaminated with the adventitious heterogeneous microorganisms by the above-described cause or any other cause becomes unsuitable for use in researches on intracrustal microorganisms.
As described above, according to the conventional method for coring a crustal core sample, measures against the microbial contamination by mixing of the adventitious heterogeneous microorganisms or growth thereof are insufficient. Therefore, the crustal core sample taken by such a method involves a problem that the sample is not fully suitable for use in researches on intracrustal microorganisms.
The present invention has been made on the basis of the foregoing circumstances and has as its object the provision of a method which has no possibility of microbial contamination from the exterior and is capable of obtaining a crustal core sample suitable for use in researches on intracrustal microorganisms.
Another object of the present invention is to provide antimicrobial polymeric gel used in this method and a gel material therefor.
According to the present invention, there is thus provided a method of taking a crustal core sample, comprising drilling the crust, wherein the crustal core sample is taken in a state coated with antimicrobial polymeric gel formed of a polymer obtained by polymerizing an antimicrobial monomer.
In this method, the antimicrobial monomer used for obtaining the polymer forming the antimicrobial polymeric gel may preferably be a quaternary ammonium salt compound, and the quaternary ammonium salt compound may preferably be at least one of an aromatic compound represented by the following general formula (1), an acryloyloxyalkyltrialkylammonium salt compound, a methacryloyloxyalkyltrialkylammonium salt compound, an acryloyloxyalkylpyridinium salt compound and a methacryloyloxyalkylpyridinium salt compound.
General Formula (1): 
wherein R1 means a linear or branched alkyl group having 1 to 18 carbon atoms, R2 and R3 are methyl groups, and Xxe2x88x92 denotes a halogen ion.
Further, the antimicrobial monomer used for obtaining the polymer forming the antimicrobial polymeric gel may also be a phosphonium salt compound. In this case, the phosphonium salt compound may preferably be an aromatic compound represented by the following general formula (2):
General Formula (2): 
wherein R4, R5 and R6 may be the same or different from one another and independently mean a linear or branched alkyl group having 1 to 18 carbon atoms, and Xxe2x88x92 denotes a halogen ion.
The polymer forming the antimicrobial polymeric gel may also preferably contain a component derived from the antimicrobial monomer in a proportion of 1 to 10 mol %.
Further, the polymer forming the antimicrobial polymeric gel may preferably be hydrophilic and be a copolymer obtained from the antimicrobial monomer and at least one of acrylamide, methacrylamide, N,Nxe2x80x2-methylenebisacrylamide and N,Nxe2x80x2-methylenebismethacrylamide.
According to the present invention, there is also provided an antimicrobial polymeric gel suitable for use in taking a crustal core sample, comprising a polymer obtained by polymerizing an antimicrobial monomer, wherein the gel is used for coating the crustal core sample upon the taking of the crustal core sample by drilling the crust.
According to the present invention, there is further provided a powdered gel material suitable for use in taking a crustal core sample, which forms antimicrobial polymeric gel by adding water thereto, wherein the antimicrobial polymeric gel is used for coating the crustal core sample upon the taking of the crustal core sample by drilling the crust.
According to such a method of taking the crustal core sample as described above, a crustal core taken out of the crust by drilling comes to be taken in a state that the whole thereof has been coated with the antimicrobial polymeric gel, whereby microbial contamination with adventitious microorganisms can be sufficiently and effectively prevented, and the growth of the adventitious microorganisms is inhibited even if the antimicrobial polymeric gel is invaded thereby. In addition, the antimicrobial polymeric gel itself is not contaminated with any microorganisms.
Since the antimicrobial polymeric gel is a polymeric material composed of a polymer, and an antimicrobial component by the antimicrobial monomer forms a part of the molecular structure thereof, the antimicrobial component is prevented from being separated and dissolved out. Accordingly, the crustal core sample obtained is not contaminated with the antimicrobial component, and so the ecological system of said crustal core sample is sufficiently protected, and moreover the antimicrobial activity or antimicrobial performance of the antimicrobial polymeric gel is exhibited stably over a long period of time.
Further, the antimicrobial polymeric gel is hydrophilic, whereby the gel has excellent affinity for the surface of the crustal core sample, and good coating property is hence achieved.
Besides, the powdered gel material suitable for use in taking a crustal core sample permits the provision of the intended antimicrobial polymeric gel with extreme ease, and is light-weight, so that its shipment and storage are extremely easy and convenient from the viewpoint of practical use.